Inorganic materials are often incorporated in composite articles to affect physical properties. In addition to increased dimensional stability, the inorganic material may improve the physical and mechanical properties of polymer composites. As one example, glass fibers may be placed into a polymer matrix to affect the strength of the composite. The high tensile strength of glass fibers may cause the composite to become more rigid. In order to improve the interfacial adhesion between glass fibers and the polymer matrix, glass fibers may be treated with a sizing composition after they are drawn from a bushing. Chemical bonding between glass fibers and the polymer matrix affects the mechanical properties and the aging performance of composite materials. However, the degree of chemical bonding at the glass-polymer interface may need to be adjusted to balance between various composite properties, including mechanical strength and fracture toughness. This and other needs are addressed in the present application.